Modular system for a belt tightener comprising a spur gear mechanism, and belt tightener

A modular system for a belt tensioner (10) comprising a spur gearing (18),

• wherein the spur gearing (18) includes at least one motor gearwheel (26) and at least a first step wheel (28) and a second step wheel (30), the motor gearwheel (26) forming a first gear stage (34) with the first step wheel (28) and the first step wheel (28) forming a second gear stage (36) with the second step wheel (30),
• wherein the modular system (11) includes plural step wheel pairings of the first step wheel (28) and the second step wheel (30),
• wherein the modular system (11) includes identically designed housings (20) into each of which a spur gearing (18) with one of the step wheel pairings can be introduced,
• wherein each first step wheel (28) and each second step wheel (30) has an opening (42) axially passing through the respective step wheel (28, 30) for holding a shaft (44), a bearing point of the housing (20) being associated with each shaft (44), and
• wherein, for each of the step wheel pairings, the number of teeth of the first step wheel (28) and the number of teeth of the second step wheel (30) are different from those of the other step wheel pairings, but the distance between the shaft (44) of the first step wheel (28) and the shaft (44) of the second step wheel (30) is equal for each of the step wheel pairings.